public class CIMMaplexGeneralPlacementProperties : CIMGeneralPlacementProperties, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

public void CreateFeatureLinkedAnnotationFeatureClass(Geodatabase geodatabase, SpatialReference spatialReference)
{
    // Creating a feature-linked annotation feature class between water pipe and valve in water distribution network
    // with following user defined fields
    // PipeName 
    // GlobalID

    // Annotation feature class name
    string annotationFeatureClassName = "WaterPipeAnnotation";

    // Create user defined attribute fields for annotation feature class
    FieldDescription pipeGlobalID = FieldDescription.CreateGlobalIDField();
    FieldDescription nameFieldDescription = FieldDescription.CreateStringField("Name", 255);

    // Create a list of all field descriptions
    List<FieldDescription> fieldDescriptions = new List<FieldDescription> { pipeGlobalID, nameFieldDescription };

    // Create a ShapeDescription object
    ShapeDescription shapeDescription = new ShapeDescription(GeometryType.Polygon, spatialReference);

    // Create general placement properties for Maplex engine 
    CIMMaplexGeneralPlacementProperties generalPlacementProperties = new CIMMaplexGeneralPlacementProperties
    {
        AllowBorderOverlap = true,
        PlacementQuality = MaplexQualityType.High,
        DrawUnplacedLabels = true,
        InvertedLabelTolerance = 1.0,
        RotateLabelWithDisplay = true,
        UnplacedLabelColor = new CIMRGBColor
        {
            R = 255,
            G = 0,
            B = 0,
            Alpha = 0.5f
        }
    };

    // Create annotation  label classes
    // Green label
    CIMLabelClass greenLabelClass = new CIMLabelClass
    {
        Name = "Green",
        ExpressionTitle = "Expression-Green",
        ExpressionEngine = LabelExpressionEngine.Arcade,
        Expression = "$feature.OBJECTID",
        ID = 1,
        Priority = 0,
        Visibility = true,
        TextSymbol = new CIMSymbolReference
        {
            Symbol = new CIMTextSymbol()
            {
                Angle = 45,
                FontType = FontType.Type1,
                FontFamilyName = "Tahoma",
                FontEffects = FontEffects.Normal,
                HaloSize = 2.0,

                Symbol = new CIMPolygonSymbol
                {
                    SymbolLayers = new CIMSymbolLayer[]
            {
        new CIMSolidFill
        {
          Color = CIMColor.CreateRGBColor(0, 255, 0)
        }
            },
                    UseRealWorldSymbolSizes = true
                }
            },
            MaxScale = 0,
            MinScale = 0,
            SymbolName = "TextSymbol-Green"
        },
        StandardLabelPlacementProperties = new CIMStandardLabelPlacementProperties
        {
            AllowOverlappingLabels = true,
            LineOffset = 1.0
        },
        MaplexLabelPlacementProperties = new CIMMaplexLabelPlacementProperties
        {
            AlignLabelToLineDirection = true,
            AvoidPolygonHoles = true
        }
    };

    // Blue label
    CIMLabelClass blueLabelClass = new CIMLabelClass
    {
        Name = "Blue",
        ExpressionTitle = "Expression-Blue",
        ExpressionEngine = LabelExpressionEngine.Arcade,
        Expression = "$feature.OBJECTID",
        ID = 2,
        Priority = 0,
        Visibility = true,
        TextSymbol = new CIMSymbolReference
        {
            Symbol = new CIMTextSymbol()
            {
                Angle = 45,
                FontType = FontType.Type1,
                FontFamilyName = "Consolas",
                FontEffects = FontEffects.Normal,
                HaloSize = 2.0,

                Symbol = new CIMPolygonSymbol
                {
                    SymbolLayers = new CIMSymbolLayer[]
            {
        new CIMSolidFill
        {
          Color = CIMColor.CreateRGBColor(0, 0, 255)
        }
            },
                    UseRealWorldSymbolSizes = true
                }
            },
            MaxScale = 0,
            MinScale = 0,
            SymbolName = "TextSymbol-Blue"
        },
        StandardLabelPlacementProperties = new CIMStandardLabelPlacementProperties
        {
            AllowOverlappingLabels = true,
            LineOffset = 1.0
        },
        MaplexLabelPlacementProperties = new CIMMaplexLabelPlacementProperties
        {
            AlignLabelToLineDirection = true,
            AvoidPolygonHoles = true
        }
    };

    // Create a list of labels
    List<CIMLabelClass> labelClasses = new List<CIMLabelClass> { greenLabelClass, blueLabelClass };


    // Create linked feature description
    // Linked feature class name
    string linkedFeatureClassName = "WaterPipe";

    // Create fields for water pipe
    FieldDescription waterPipeGlobalID = FieldDescription.CreateGlobalIDField();
    FieldDescription pipeName = FieldDescription.CreateStringField("PipeName", 255);

    // Create a list of water pipe field descriptions
    List<FieldDescription> pipeFieldDescriptions = new List<FieldDescription> { waterPipeGlobalID, pipeName };

    // Create a linked feature class description
    FeatureClassDescription linkedFeatureClassDescription = new FeatureClassDescription(linkedFeatureClassName, pipeFieldDescriptions,
      new ShapeDescription(GeometryType.Polyline, spatialReference));

    // Create a SchemaBuilder object
    SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

    // Add the creation of the linked feature class to the list of DDL tasks
    FeatureClassToken linkedFeatureClassToken = schemaBuilder.Create(linkedFeatureClassDescription);

    // Create an annotation feature class description object to describe the feature class to create
    AnnotationFeatureClassDescription annotationFeatureClassDescription =
      new AnnotationFeatureClassDescription(annotationFeatureClassName, fieldDescriptions, shapeDescription,
        generalPlacementProperties, labelClasses, new FeatureClassDescription(linkedFeatureClassToken))
      {
          IsAutoCreate = true,
          IsSymbolIDRequired = false,
          IsUpdatedOnShapeChange = true
      };

    // Add the creation of the annotation feature class to the list of DDL tasks
    schemaBuilder.Create(annotationFeatureClassDescription);

    // Execute the DDL
    bool success = schemaBuilder.Build();

    // Inspect error messages
    if (!success)
    {
        IReadOnlyList<string> errorMessages = schemaBuilder.ErrorMessages;
        //etc.
    }
}

public static void CreateDictionary()
{
  //Get the map's definition
  var mapDefn = MapView.Active.Map.GetDefinition();
  //Get the Map's Maplex labelling engine properties
  var mapDefnPlacementProps = mapDefn.GeneralPlacementProperties as CIMMaplexGeneralPlacementProperties;

  //Define the abbreviations we need in an array            
  List<CIMMaplexDictionaryEntry> abbreviationDictionary = new List<CIMMaplexDictionaryEntry>
        {
            new CIMMaplexDictionaryEntry {
            Abbreviation = "Hts",
            Text = "Heights",
            MaplexAbbreviationType = MaplexAbbreviationType.Ending

         },
            new CIMMaplexDictionaryEntry
            {
                Abbreviation = "Ct",
                Text = "Text",
                MaplexAbbreviationType = MaplexAbbreviationType.Ending

            }
            //etc
        };
  //The Maplex Dictionary - can hold multiple Abbreviation collections
  var maplexDictionary = new List<CIMMaplexDictionary>
        {
            new CIMMaplexDictionary {
                Name = "NameEndingsAbbreviations",
                MaplexDictionary = abbreviationDictionary.ToArray()
            }

        };
  //Set the Maplex Label Engine Dictionary property to the Maplex Dictionary collection created above.
  mapDefnPlacementProps.Dictionaries = maplexDictionary.ToArray();
  //Set the Map definition 
  MapView.Active.Map.SetDefinition(mapDefn);
}

private static void ApplyDictionary()
{
  var featureLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>().First();

  QueuedTask.Run(() =>
  {
    //Creates Abbreviation dictionary and adds to Map Definition                                
    CreateDictionary();
    //Get the layer's definition
    var lyrDefn = featureLayer.GetDefinition() as CIMFeatureLayer;
    //Get the label classes - we need the first one
    var listLabelClasses = lyrDefn.LabelClasses.ToList();
    var theLabelClass = listLabelClasses.FirstOrDefault();
    //Modify label Placement props to use abbreviation dictionary 
    CIMGeneralPlacementProperties labelEngine = MapView.Active.Map.GetDefinition().GeneralPlacementProperties;
    theLabelClass.MaplexLabelPlacementProperties.DictionaryName = "NameEndingsAbbreviations";
    theLabelClass.MaplexLabelPlacementProperties.CanAbbreviateLabel = true;
    theLabelClass.MaplexLabelPlacementProperties.CanStackLabel = false;
    //Set the labelClasses back
    lyrDefn.LabelClasses = listLabelClasses.ToArray();
    //set the layer's definition
    featureLayer.SetDefinition(lyrDefn);
  });
}

//Note: call within QueuedTask.Run()

//Get the active map's definition - CIMMap.
var cimMap = MapView.Active.Map.GetDefinition();
//Get the labeling engine from the map definition
var cimGeneralPlacement = cimMap.GeneralPlacementProperties;

if (cimGeneralPlacement is CIMMaplexGeneralPlacementProperties)
{
  //Current labeling engine is Maplex labeling engine
  //Create a new standard label engine properties
  var cimStandardPlacementProperties = new CIMStandardGeneralPlacementProperties();
  //Set the CIMMap's GeneralPlacementProperties to the new label engine
  cimMap.GeneralPlacementProperties = cimStandardPlacementProperties;
}
else
{
  //Current labeling engine is Standard labeling engine
  //Create a new Maplex label engine properties
  var cimMaplexGeneralPlacementProperties = new CIMMaplexGeneralPlacementProperties();
  //Set the CIMMap's GeneralPlacementProperties to the new label engine
  cimMap.GeneralPlacementProperties = cimMaplexGeneralPlacementProperties;
}
//Set the map's definition
MapView.Active.Map.SetDefinition(cimMap);